Quick Question - Heat Shrink on 3mm LED/LDR size?

Kevin Mitchell · October 15, 2015, 02:28:29 PM

About to pull the trigger on another parts order and I just remembered that I've been wanting to snag some heat shrink. Would be very useful since I breadboard and experiment with LFOs weekly pretty much.

What guage or better yet - diameter of heatshrink would be appropriate for 3mm leds to standard small LDRs?

Don't want to buy the wrong thing

. Radio Shack has assortments them but are RIDICULOUSLY overpriced.

armdnrdy · October 15, 2015, 02:36:47 PM

Heat shrink slightly larger than the diameter of the LDR you are using.

Look at the data sheet or...it you have the LDRs in your possession...measure them.

Kevin Mitchell · October 15, 2015, 02:43:18 PM

I'm not around any of my supplies but if I'm using 3mm LEDs ~(.118") then something like the available .125" should be snug. Or is that too snug once shrunk?

There's also .1875" but I don't know if that would shrink snug enough?

Ehh 30 cent a foot isn't a big deal. But still it would be nice to know.

armdnrdy · October 15, 2015, 03:00:07 PM

LDRs are generally larger diameter than 3mm LEDs.

I think that the smaller LDRs are about 5mm.

Kevin Mitchell · October 15, 2015, 03:10:37 PM

Maybe 5mm one way and like 3.5mm the other way since they're not symmetrical. Idk lol. I'll snag a few sized. .25" as well. I'm sure all of it would be used for wiring and such anyway.

Thank you for your thoughts!

davent · October 15, 2015, 04:14:39 PM

Heatshrink is usually 2:1 or the good stuff, 3:1 shrink, so those would be your upper limits.

Cozybuilder · October 15, 2015, 06:02:00 PM

For 3mm LEDs and the Tayda LDRs (GL5537) I use black ¼" heatshrink- it works fine.

Kipper4 · October 15, 2015, 07:11:41 PM

/\ Me too but mostly with 5mm leds

anotherjim · October 16, 2015, 04:34:20 AM

I think flat top round 5mm leds make a neater job.
BTW, used on a breadboard circuit, it matters if light can get in the ends of the shrink tube. While the shrink is hot, you can pinch the ends of the tubing between the leads with needle nose pliers and it'll stay put when cool. That stops most of the light getting in, but not perfectly.

There is this stuff, used in professional cable work that's like a black bitumen tape (like blue tack - but black). Anyway, you pull off a chunk and stuff it between the cable cores at the exit from the sheath before sealing it tidy with a piece of heat-shrink. Makes a neat, moisture-proof cable end. I think it would be perfect for sealing the ends of DIY Vactrols, but I have no idea what it's really called or how to get it!

greaser_au · October 16, 2015, 06:07:42 AM

Quote from: anotherjim on October 16, 2015, 04:34:20 AM
There is this stuff, used in professional cable work that's like a black bitumen tape (like blue tack - but black). Anyway, you pull off a chunk and stuff it between the cable cores at the exit from the sheath before sealing it tidy with a piece of heat-shrink. Makes a neat, moisture-proof cable end. I think it would be perfect for sealing the ends of DIY Vactrols, but I have no idea what it's really called or how to get it!

do you mean 'self-amalgamating tape'?

david

Cozybuilder · October 16, 2015, 09:03:16 AM

You can use a drop of black RTV to seal the ends too, and using 2 3mm LEDs still makes a small package

anotherjim · October 16, 2015, 10:58:09 AM

"do you mean 'self-amalgamating tape'?"

Probably the same stuff, yes, but I think it was thicker.

Has RTV changed? I remember when it first came out - a friend used it to seal a pcb in a potting box (didn't have any resin) and it all went green and shorted out! I was told it releases acid as it cures.

Cozybuilder · October 16, 2015, 11:33:43 AM

Maybe I called it the wrong thing, its "Permatex Black Silicone Adhesive Sealant", item#81158(16B), new low odor formulation. Ingredients list calcium carbonate & petroleum distillates- this doesn't smell like acetic acid, which would do what your friend experienced. I have had no problems using it.

armdnrdy · October 16, 2015, 11:51:51 AM

A few years back, I researched potential issues with using silicone based sealants with electronics.

As usual...there is some good information available on the net.

http://forum.allaboutcircuits.com/threads/silicone-gel-as-an-insulator-conductive.45001/

greaser_au · October 16, 2015, 04:44:25 PM

I made some general comments about RTV silicone for electronic uses here a few years back - this was in reference to use as an adhesive, but the main paragraph is relevant here I think...

The trick is being able to identify the non-acid-cure stuff from the blurb before you buy it & open the tube!

david

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Quick Question - Heat Shrink on 3mm LED/LDR size?